This disclosure relates to test and measurement instruments, in particular to test and measurement instruments having an automatic threshold control.
Test and measurement instruments can use a comparator to sense a logic level of an input signal. For example, a logic analyzer is designed to sample digital data. Such digital data can have logic levels represented by different voltage levels. To determine the logic level of the digital data, the logic analyzer compares the input signal to a threshold. When the signal is on one side of the threshold, the input signal is interpreted as a first one of the logic levels such as a zero. When the input signal is on another side of the threshold, the input signal is interpreted as a second one of the logic levels such as a one.
However, different logic families can have different levels and corresponding different thresholds. Moreover, a threshold for a particular level of performance may need to be offset from an theoretical value such as half-way between two logic levels.
A user can manually set such a threshold. Alternatively, a logic analyzer can acquire a series of samples of an input signal for a variety of thresholds. Once the multiple series of sampled data arc acquired, a determination can be made on boundaries between transitioning data and steady state data. A threshold can be selected that is between the boundaries.